NEW FORMATION MECHANISM OF ELECTRIC-FIELD DOMAIN DUE TO GAMMA-X SEQUENTIAL TUNNELING IN GAAS/ALAS SUPERLATTICES

We have studied the sequential tunneling of doped weakly coupled GaAs/ALAs superlattices (SLs), whose ground state of the X valley in AlAS layers is designed to be located between the ground state (E(GAMMA1)) and the first excited state (E(GAMMA2)) of the GAMMA valley in GaAs wells. The experimental results demonstrate that the high electric field domain in these SLs is attributed to the GAMMA-X sequential tunneling instead of the usual sequential resonant tunneling between subbands in adjacent wells. Within this kind of high field domain, electrons from the ground state in the GaAs well tunnel to the ground state of the X valley in the nearest AlAs layer, then through very rapid real-space transfer relax from the X valley in the AlAs layer to the ground state of the GAMMA valley of the next GaAs well.

A transition layer model and its application to resonant tunneling in heterostructures

A transition layer model is proposed and used to calculate resonant tunneling in a double-barrier quantum well system. Compared with the ideal step of the potential at the interface, the studied system has transition layers that are composed by many thin rectangular barriers with a random height. It is found that these transition layers can improve the peak-to-valley ratio of the tunneling current and change the negative differential conductance.

小孔径蝴蝶型光电导天线太赫兹辐射源的研究

研究了5种小孔径光电导天线的太赫兹发射特性,并且对它们所发射的太赫兹波进行了对比,为研制高效率的太赫兹波发射源提供了参考依据。利用太赫兹时域光谱技术测量了光电导天线发射的太赫兹(THz)脉冲,得到了时域发射光谱,并通过快速傅里叶变换得到相应的频域光谱。结果表明,太赫兹信号强度随偏置电压的增大而增强;随着泵浦激光功率的增大而增强并出现饱和现象。偏置电压与泵浦激光功率相同时,我们对比5种光电导天线产生的太赫兹信号,从中找到了一种发射效率较高的小孔径光电导天线,并且研究了电极形状、电极间距对光电导天线发射效率的影响。

A面(11-20)ZnO薄膜中杂质的偏振PL谱研究

本文通过分析A面(11-20)ZnO薄膜的低温PL(光致发光)光谱偏振特性来研究ZnO光致发光谱中杂质峰的来源.低温(4 K)下观察到476、479 nm两处新的杂质峰以及390 nm处激子峰,根据两个杂质峰的偏振特性,初步判定476nm峰来源于氧空位能级到价带轻空穴的跃迁,479 nm峰来源于氧空位价带重空穴的跃迁.

基于仿生模式识别理论的高阶神经网络说话人识别方法

根据一种全新的仿生模式识别理论,提出了采用神经网络实现并完成说话人识别的新方法.该方法利用高阶神经网络形成的复杂包络在特征空间中构造不同说话人的覆盖区域达到识别目的.相关实验证明,这种新的说话人识别方法只要通过少量样本的训练即可达到比传统方法更高的识别率.

应变异质结外延材料的缓冲层厚度与Frank-Read源的关系研究

基于能量最小近似模型,研究了应变异质结外延材料中,产生Frank-Read源以释放失配应力所需GeSi合金缓冲层的厚度。对Ge_xSi_(1-x)/Si进行了具体计算,其结果表明:产生Frank-Read源时缓冲层厚度要比临界厚度大得多,L_(min)=1300A是钉扎点间的最小距离。计算结果与LeGoues等的实验结果相符。就作者所知,计算产生Frank-Read源时GeSi合金缓冲层厚度的工作,以前未见报道。

基于红外光谱技术的经皮二氧化碳分压检测仪的设计原理与可行性研究

于2010-11-23批量导入

Au、Al/a-Si:H热退火行为研究

于2010-11-23批量导入

Potential light source for photonic integrated circuits based on the equilateral triangle resonator

The semiconductor microlasers based on the equilateral triangle resonator (ETR) can be fabricated from the edge-emitting laser wafer by dry-etching technique, and the directional emission can be obtained by connecting an output waveguide to one of the vertices of the ETR. We investigate the mode characteristics, especially the mode quality factor, for the ETR with imperfect vertices, which is inevitable in the real technique process. The numerical simulations show that the confined modes can still have a high quality factor in the ETR with imperfect vertices. We can expect that the microlasers is a suitable light source for photonic integrated circuits.

中国裂叶苔科植物的研究-分类、区系和生态

裂叶苔科（Lophoziaceae）是叶苔目植物中的一个大科，其植物体形态变化较大，分类较为困难。中国在裂计佩一苔科下已记录的植物有23属、106种、2变种和2变形。本论文在大量文献考证和对国内外3000余份标本深入研究基础上，对中国裂仆佩一苔科进行了较系统全面的分类修订，记录了中国裂价卜苔科植物共有11属45种3变种1变形，提供了种属形态特征描述和41幅图版。发现中国新记录2种1变型：异瓣裂叶苔（Lophozia diversiloba Hatt），毛口挺叶苔（Anastrophyllum piligerm (Nees.) Steph.）和密叶三瓣苔小叶变形（Tritomaria quinquedentata fo. gracilis (Jens.) Schust.）；新组合名1个：小挺叶苔尖变种（Anastrophyllum minutum (Schreb. in Cranz.) Schust var. acuminatum (Horik.) Cao & Sun comb. nov.），还有省区新分布记录16个。采用聚类分析方法分析了裂叶苔科种属间的关系，结果支持广义裂汗卜苔属和挺口一卜苔属的概念。 区系成分的分析研究表明：中国裂计佩一苔科植物的地理成分主要以泛北极分布类型为主，占79.6%.东北地区、秦岭地区、西南地区和台湾省为我国裂p_佩一苔科植物种类最丰富的地区。在国内首次开展了苔类专科的生态学研究，并采用CCA方法对结果进行分析。研究表明：裂叶苔科植物在长白山分布上表现出明显的垂直地带性，可分为三类：（1)分布在2000米以上苔原带的种类，主要有小挺叶苔A. minutum、石生挺叶苔A. saxicola、密叶三瓣苔T. quinquedentata、高山裂叶苔L. sudetica，圆叶裂叶L. wenzelii；（2）分布在1730米到2000米苔岳桦林带的种类，主要有：方叶无褶苔L. bantriensis，细裂瓣苔B. barbata，阔瓣裂叶苔L. excisa；（3）分布在1150-1730米以下暗针叶林的种类，主要有：三瓣苔T. exsecta，多角胞三瓣苔T. exsectiformis、囊苞裂叶苔L. ventricosa，秃瓣裂叶苔L. obtusa和倾立裂叶苔L. ascendens。影响裂叶苔科植物分布的主要坏境因子是海拔高度。 对处于不同纬度三个地区的同种裂叶苔科植物的比较分析说明：随纬度的升高其分布的海拔高度逐步降低。